Stabilized knee prosthesis

ABSTRACT

A knee prosthesis includes a femoral component, a tibial component, and a coupling component interconnecting the femoral component and the tibial component. The tibial component includes ball. The femoral component is configured to move relative to the tibial component. The coupling component defines an internal cavity including a first spherical end portion and a second spherical end portion. The internal cavity is dimensioned to receive the ball of the tibial component. The ball is repositioned between the first spherical end portion and the second spherical end portion of the internal cavity upon movement of the femoral component relative to the tibial component.

BACKGROUND OF THE INVENTION

The present disclosure relates to orthopedics devices and, moreparticularly, to knee prostheses.

During articulation of a natural knee joint, flexion between the tibiaand the femur takes place about a transverse axis while some relativerotation between the tibia and the femur occurs about a longitudinalaxis. Such flexion and rotation is necessary to carry out a normal gatecycle. It has been established that in full extension the tibia isrotationally displaced, relative to the femur, by approximately 2-3degrees. As the natural knee flexes, the tibia rotates internally.According to previous studies, about 5 degree of rotation ordinarilyoccurs as the knee is articulated from 0 degree to 10 degree of flexion;thereafter, little further rotation occurs up to at least about 45degree of flexion. Total rotation at 110 degrees of flexion isapproximately 20 degrees.

Rotational stability of the natural knee is provided by the collateraland cruciate ligaments. The cruciate ligaments deter uncontrolledinternal rotation within a certain range of flexion of the knee, whilethe collateral ligaments provide transverse stability and deteruncontrolled external rotation of the tibia. Where the natural knee isreplaced by a total knee prosthesis, either the anterior cruciateligament or both the anterior and posterior cruciate ligamentsordinarily are sacrificed. In the instances where the knee prosthesis isconstrained to supply the stability ordinarily provided by thesacrificed ligaments, it is desirable for the knee prosthesis to mimicthe natural knee as closely as possible.

Although several knee prostheses have been developed over the years,improvements are still possible. A need exists for knee prosthesescapable of more closely imitating the natural knee.

As used herein, when referring to bones or other parts of the body, theterm “proximal” means closer to the heart and the term “distal” meansmore distant from the heart. The term “inferior” means towards the feetand the term “superior” means towards the head. The term “anterior”means towards the front part of the body or the face and the term“posterior” means towards the back of the body. The term “medial” meanstowards the midline of the body and the term “lateral” means away fromthe midline of the body.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to a knee prosthesis for implantation ina knee joint. In one embodiment, the knee prosthesis includes a femoralcomponent, a tibial component, and a coupling component mounted on thefemoral component and interconnecting the femoral component and thetibial component. The tibial component includes a ball. The femoralcomponent is configured to move relative to the tibial component. Thecoupling component defines an internal cavity including a firstspherical end portion and a second spherical end portion. The internalcavity is dimensioned to receive the ball of the tibial component. Theball is repositioned between the first spherical end portion and thesecond spherical end portion of the internal cavity upon movement of thefemoral component relative to the tibial component.

In an alternate embodiment, the knee prosthesis includes a femoralcomponent, a tibial component including a ball and a coupling component.The femoral component is configured to articulate relative to the ballof the tibial component. The coupling component connects the femoralcomponent to the tibial component and defines an internal cavityincluding a first cavity portion and a second cavity portion. Each ofthe first and second cavity portions is dimensioned to receive the ball.The first and second cavity portions are in communication with eachother. The coupling component moves upon articulation of the femoralcomponent relative to the tibial component between a first positionwhere the ball is positioned in the first cavity portion and a secondposition where the ball is positioned in the second cavity portion.

In an alternate embodiment, the knee prosthesis includes a femoralcomponent, a tibial component, and a coupling component movablyinterconnecting the femoral component to the tibial component. Thefemoral component includes a housing with an anterior wall. The couplingcomponent includes a first post and a second post at least partiallypositioned within the first post. The first post has a protrusionconfigured to engage the anterior wall of the housing duringhyperextension of a knee. The coupling component may be monolithicallyformed with at least a portion of the tibial component.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood with reference to thefollowing drawings and description. The components in the figures arenot necessarily to scale, emphasis instead being placed uponillustrating the principles of the presently disclosed knee prosthesis.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1. is an isometric cut-away view of a knee prosthesis according toan embodiment of the present disclosure;

FIG. 2 is a cross-sectional view, taken along a plane parallel to thecoronal plane, of the knee prosthesis of FIG. 1;

FIG. 3 is an isometric view of a tibial baseplate of the knee prosthesisof FIG. 1;

FIG. 4 is an isometric view of a tibial insert of the knee prosthesis ofFIG. 1;

FIG. 5 is an isometric view of a tibial component including the tibialbaseplate and the tibial insert assembled together;

FIG. 6 is an isometric proximal view of a femoral component of the kneeprosthesis of FIG. 1;

FIG. 7 is an isometric distal view of the femoral component of FIG. 6;

FIG. 8 is a side cross-sectional view of a coupling component of theknee prosthesis of FIG. 1;

FIG. 9 is an isometric view of the coupling component of FIG. 8;

FIG. 10 is a side cross-sectional view of the knee prosthesis of FIG. 1in full extension;

FIG. 11 is a side cross-sectional view of the knee prosthesis of FIG. 1in a 20 degree extension;

FIG. 12 is a side cross-sectional view of the knee prosthesis of FIG. 1in a 90 degree extension;

FIG. 13 is a side cross-sectional view of the knee prosthesis of FIG. 1in a 110 degree extension;

FIG. 14 is a side cross-sectional view of the knee prosthesis of FIG. 1in a 135 degree extension;

FIG. 15 is a superior view of the knee prosthesis of FIG. 1;

FIG. 16 is a cross-sectional view, taken along a plane parallel to thecoronal plane, of another embodiment of the knee prosthesis;

FIG. 17 is a perspective sectional view of a further embodiment of theknee prosthesis with a protrusion on the post anterior surface;

FIG. 18 is another perspective sectional view of the embodiment of theknee prosthesis depicted in FIG. 17;

FIG. 19 is a perspective view of a tibial baseplate of the kneeprosthesis shown in FIG. 17;

FIG. 20 is a perspective view of a femoral component of the kneeprosthesis of FIG. 17;

FIG. 21 is a perspective view of a connecting post with a bumperintegrally formed therewith;

FIG. 22 is a perspective view of a support post for providing support tothe connecting post of FIG. 21;

FIG. 23 is a perspective view of a tibial insert of the knee prosthesisof FIG. 17;

FIG. 24 is a perspective sectional view of a knee prosthesis of FIG. 17in hyperextension, showing the bumper of the connecting post engaging aportion of the femoral component;

FIG. 25 is a perspective view of a tibial insert with an integrallyformed connecting post; and

FIG. 26 is a side sectional view of the tibial insert of FIG. 25.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict an embodiment of a stabilized knee prosthesis 100for replacing a natural knee joint. In some embodiments, knee prosthesis100 includes a femoral component 102, a tibial component 104, and acoupling component 106 interconnecting the femoral component 102 andtibial component 104. In operation, femoral component 102 can articulaterelative to tibial component 104 or bearing component 116 and couplingcomponent 106 rotates with femoral component 102, as discussed in detailbelow. Coupling component 106 controls the rotation of the femoralcomponent 102 as it articulates in relation to tibial component 104.Femoral component 102 has condyles that articulate on the condylartracks of the bearing component 116 of the tibial component 104. Tibialcomponent 104 is adapted to be attached to a proximal end of a tibia,whereas femoral component 102 is adapted to be attached to a distal endof a femur in a well known manner. Both the distal end of the femur andthe proximal end of the tibia may be resected or prepared beforeimplantation of knee prosthesis 100. In some embodiments, kneeprosthesis 100 is wholly or partly made of a substantially rigidmaterial, such as titanium, titanium alloy, chrome-cobalt alloy,cobalt-chromium-molybdenum alloys (e.g., cobalt-chromium-molybdenumalloy sold under the trademark Vitallium®), polyethylene, polyetherether ketone (PEEK), or any suitable metal or polymer. Bearing component116 is primarily made of ultra high molecular weight polyethylene(UHMWPE).

Tibial component 104 includes a ball or spherical member 108 forfacilitating articulation of femoral component 102 relative to tibialcomponent 104. Ball 108 may have a spherical shape or any other suitableshape (e.g., oblong shape). Coupling element 106 substantially enclosesor surrounds ball 108 of tibial component 104. Femoral component 102surrounds at least a portion of coupling component 106. In someembodiments, femoral component 102 substantially encloses couplingcomponent 106. In any case, femoral component 102 is fixed relative tocoupling component 106 and, consequently, femoral component 102 andcoupling component 106 move concomitantly.

With reference to FIG. 3, tibial component 104 includes a baseplate 110incorporating an intercondylar support 111 to support, among otherthings, a post 118 attached to ball 108. Baseplate 110 may have asubstantially oblong shape matching the proximal tibia and includes adistally facing bone contacting bottom portion 112 for engaging theproximal tibia and a proximally facing top portion 114 for engaging andsupporting a tibial bearing insert or component 116 (see FIG. 4). Thetop portion 114 of baseplate 110 includes sides 126, 127 defining anopening 119 for supporting tibial bearing insert 116. Sides 126, 127 ofbaseplate 110 are oriented in directly opposite relationship withrespect to each other and are oriented medially or laterally dependingon whether the baseplate 110 is on the left or right tibia. In addition,sides 126, 127 of baseplate 110 include extensions 121 and 123 forlocking tibial bearing insert 116 on baseplate 110. Central support 111extends into opening 119 defined by baseplate 110. Support 111 assistsin locating tibial bearing insert 116 when tibial bearing insert 116 isassembled with baseplate 110. Opening 119 is dimensioned for receivingthe bottom surface 128 of tibial bearing insert 116, shown in FIG. 4.Connecting post 118 extends from support 111 and couples ball 108 tobaseplate 110. In particular, connecting post 118 has a first end 122connected to support 111 and a second end 124 connected to ball 108. Insome embodiments, connecting post 118 has a substantially cylindricalshape. Irrespective of its shape, connecting post 118 is made wholly orpartly of a substantially rigid material. Post 118 may be modular and/orball 108 may have different sizes to provide variation in theproximal-distal location of ball 108.

As shown in FIG. 4, tibial component 104 further includes a tibialbearing insert 116 for facilitating articulation of femoral component102 relative to tibial component 104. Tibial bearing insert 116 includesa side portions 129, 131 and a distally facing bottom portion 128 forsecurely engaging the top portion 114 of baseplate 110 and a proximallyfacing top portion 130 for providing a bearing surface for supporting atleast a condylar portion of femoral component 102. First and secondportions 128, 130 are oriented in a directly opposite relationship toeach other. Top portion 130 has a first depression or undulation ormedial condyle track 132 and a second depression or undulation orlateral condyle track 134. Each of first and second undulations 132, 134is adapted to receive and support a condyle of femoral component 102.Between first and second respective condylar depressions 132, 134,tibial insert 116 defines a clearance slot 136 dimensioned for securelyreceiving connecting post 118 of baseplate 110.

Clearance slot 136 facilitates assembly of tibial bearing insert 116onto baseplate 110. During assembly, distal side 128 of tibial bearinginsert 116 is placed and locked to proximal surface 114 of baseplate 110via extensions 121, 123. Connecting post 118 is allowed to pass throughclearance slot 136. After assembly, a distal portion of connecting post118 is received within clearance slot 136, as seen in FIG. 5. FIG. 5also shows that, in an assembled tibial component 104, ball 108 isspaced proximally from tibial bearing insert 116.

Referring to FIGS. 6 and 7, femoral component 102 includes a proximalfirst side 138 for securely engaging the distal end of a distal femurand a second side 140 oriented in a directly opposite relationship tofirst side 138 and forming the condylar bearing surface of femoralcomponent 102. Second side 140 of femoral component 102 includes a firstor medial condyle 142 and a second or lateral condyle 144. As seen inFIG. 7, first and second condyles 142, 144 have the typical arcuateconfiguration and are oriented substantially parallel to each other. Asdiscussed above, first and second condyle tracks 132, 134 are configuredto receive first and second condyles 142, 144, respectively. Second side140 of femoral component 102 further includes a anteriorly facingpatella track 146 located between first and second condyles 142, 144 andadapted to receive a patellar implant (not shown).

First or proximally facing side 138 of femoral component 102 furtherincludes a proximally extending housing 148 located on a proximal facingsurface of a distal region of femoral component 102 and between firstand second condyles 142, 144. Housing 148 includes a medial wall 150adjacent to medial condyle 142, a lateral wall 152 adjacent to lateralcondyle 144, an anterior wall 154 and a proximal wall 156. Anterior andproximal walls 154, 156 both connect the medial and lateral walls 150,152. Housing 148 defines an opening 158 dimensioned for receivingcoupling component 106 and at least a portion of connecting post 118.Opening 158 is located in the posterior region of the femoral component102 between medial and lateral condyles 142, 144. Walls 150, 152 offemoral component 102 include guide slots apertures 159, which functionwill be discussed below.

With reference to FIGS. 8 and 9, there is shown a coupling component 106which is mounted on femoral component 102 and receives ball 108, whichconnects femoral component 102 to tibial component 104. In someembodiments, coupling component 106 may have two parts such as firstsection 160 and a second section 162, but coupling component 106 may beformed of a one-piece monolithic structure. First and second sections160, 162 may be symmetrical halves or asymmetrical parts. In any case,first and second sections 160, 162 collectively form coupling component106. In the embodiment depicted in FIG. 9, coupling component 106defines a centrally located slot 180 between first and second sections160, 162. As seen in FIG. 2, slot 180 is dimensioned to closely fitconnecting post 118. In addition to slot 180, coupling component 106 hasan outer surface 164 adapted for securely engaging housing 148 offemoral component 102 and forms an internal pocket or cavity 166dimensioned for receiving ball 108 of tibial component 104. Couplingcomponent 106 further includes a pair of extensions 169 which arereceived within apertures 159 of housing 148. Extensions 169 extendoutwardly from outer surface 164.

As best seen in the cross-section of FIG. 8, internal cavity 166includes a first cavity portion or spherical end portion 168, a secondcavity portion or spherical end portion 170, and a longitudinal portion172 coupling the first and second spherical end portions 168, 170. Incertain embodiments, longitudinal portion 172 has a substantiallycylindrical shape. First and second cavity portions 168, 170 may have aspherical shape as well as any other suitable shapes. The sphericalshape of cavity end portions 168, 170 may match ball 108. Longitudinalportion 172, first spherical end portion 168 and second spherical endportion 170 may have substantially similar or identical diameters toallow a smooth reposition of ball 108 within internal cavity 166 duringarticulation of femoral component 102 in relation to tibial component104. Internal cavity 166 also includes an elongated portion 177dimensioned for receiving at least a portion of connecting post 118.

Coupling component 106 defines a slot 180 adjacent to internal cavity166. Slot 180 terminates at two ends (i.e., a first end 174 and a secondend 176.) First end 174 may have a radius of about one-half the width ofslot 180. Second end 176 includes a series of curved surfaces defining acam 178. Cam 178 is configured to engage connecting post 118 uponarticulation of femoral component 102 relative to tibial component 104.When cam 178 engages connecting post 118, ball 108 is repositioned fromfirst spherical end portion 168 to second spherical end portion 170 dueto the movement of femoral component 102 with respect to tibialcomponent 104 from extension to flexion, as discussed in detail below.

As seen in FIGS. 10-14, knee prosthesis 100 substantially mimics thekinematics of the natural knee because of the location of ball 108 withrespect to the flexion axis and the rotary arc. U.S. Pat. No. 7,160,330,the entire contents of which are incorporated herein by reference,describes in detail the flexion axis and the rotary arc. When kneeprosthesis 100 is implanted in a patient, femoral component 102articulates with respect to tibial component 104 during flexion. Duringflexion of knee prosthesis 100, coupling component 106 moves along withfemoral component 102 and, consequently, ball 108 is repositionedbetween a first position in full extension and a second position in fullflexion. In the first extended position, ball 108 is located inspherical end portion 168, as seen in FIG. 10. In the second flexedposition, ball 108 is located in spherical end portion 170, as shown inFIG. 14. While knee prosthesis 100 flexes from extension to fullflexion, ball 108 is situated in a plurality of positions between thefirst and second spherical end portions 168 and 170. Thus, ball 108 maybe located at least partially at various positions along longitudinalportion 172 of internal cavity 166 between first and second sphericalend portions 168, 170, as depicted in FIG. 13.

FIG. 10 shows femoral component 102 in full extension with respect totibial component (i.e., 0 degree flexion). In the full extensionposition, ball 108 of tibial component 104 is located in first sphericalend 168 of internal cavity 166. As seen in FIG. 10, when knee prosthesis100 has an open space 125 between connecting post 118 and couplingcomponent 106 that allows hyperextension (e.g., 15 degrees) of the knee.When femoral component 102 rotates 20 degree (i.e., 20 degree flexion)relative to tibial component 104, as seen in FIG. 11, ball 108 remainsin the first spherical end portion 168 of internal cavity 166. Asfemoral component 102 moves between 20 and 135 degrees of flexion, theflexion axis of the medial and lateral condyles 142, 144 coincides withthe centerline of ball 108. The alignment between the flexion axis ofthe medial and lateral condyles 142, 144 and the centerline of ball 108facilitates smooth rotation and allows compressive loads to betransferred to the articular surface of the tibia throughout the rangeof motion. Despite facilitating movement, this alignment prevents, or atleast inhibits, anterior-posterior (“A-P”) displacement, because ball108 is captured in first spherical end portion 168 of internal cavity166. In any event, the position of ball 108 allows flexion, reasonablyrestoring the function of the cruciate ligaments. As seen in FIG. 15,the centerline of ball 108 is aligned with the center plane of rotaryarc A defined the trajectory of femoral component 102 with respect totibial component 104. Such alignment allows the femur to internally andexternally rotate as required during flexion and extension.

Knee prosthesis 100 may be assembled prior or during an operation. Allcomponents of knee prosthesis 100 are sized so that they can be snappedtogether. Accordingly, operators may assemble knee prosthesis 100without any tools. In one exemplary method of assembly, an operatorsnaps the first side 128 of tibial bearing insert 116 onto the proximalsurface 114 of baseplate 110 via extensions 121, 123, thereby lockingtibial bearing insert 116 to baseplate 110 as seen in FIG. 5. Whiletibial bearing insert 116 is being locked to baseplate 110, theconnecting post 118 of baseplate 110 is allowed to pass through theclearance slot 136 of tibial bearing insert 116. Coupling component 106can also be mounted within the housing 148 of femoral component 102. Tothis end, the operator may slide extensions 169 of coupling component106 through elongated apertures 159 of housing 148 until couplingcomponent 106 is securely attached to femoral component 102. Ball 108 ofbaseplate 110 is then snapped into the internal cavity 166 of couplingcomponent 106. As discussed in detail below, knee prosthesis 100 may usedifferent kinds of coupling components. These coupling components 106can be changed before or during an operation.

In one exemplary method of use, ball 108 remains in the first sphericalend portion 168 of internal cavity 166 when femoral component 102rotates between 20 degree of flexion (FIG. 11) and 90 degree of flexion(FIG. 12). At 90 degree of flexion, cam 178 of coupling component 106engages or contacts connecting post 118 of tibial component 104. Whilefemoral component 102 rotates from the 90 degree of flexion to 110degree of flexion (FIG. 13), femoral component 102 begins to roll backwith respect to tibial component 104 when cam 178 engages connectingpost 118. For example, femoral component 102 may roll back a distance Xwith respect to tibial component 104, thereby changing the position ofball 108 relative to internal cavity 166. As femoral component 102 rollsback, coupling component 106, which is fixed to femoral component 102,rolls back as well and displaces internal cavity 166 relative to thetibial component 104. The displacement of internal cavity 166 causes therelocation of ball 108. Specifically, ball 108 gradually relocates fromfirst spherical end portion 168 to second spherical end portion 170. Forexample, in the 110 degree of flexion, ball 108 is partially positionedin the longitudinal portion 172 of internal cavity 166 between the firstand second spherical end portions 168, 170 of internal cavity 166. Whilefemoral component 102 rotates from 110 degree of flexion to 135 degreeof flexion, femoral component 102 rolls back further (i.e., a distanceY), displacing internal cavity 166 relative to ball 108. Distance Y isgreater than distance X. In the 135 degree of flexion, ball 108 ispositioned in the second spherical end portion 170 of internal cavity166. Although the drawings show the femoral component 102 articulatingrelative to the tibial component between 20 and 135 degrees of flexion,the femoral component 102 can articulate up to 150 degrees of flexion.

FIG. 16 shows knee prosthesis 100 with an alternate coupling component106 a. Coupling component 106 defines a slot 180 a that does not closelyfits connecting post 118. In this embodiment, slot 180 a may have adiameter substantially similar or equal to the diameter of ball 108.Coupling component 106 a does not resist varus or valgus moment.

Which coupling component 106, 106 a is selected depends on the level ofvarus/valgus constraint required for the patient, which in turn is basedon the health and function of the collateral ligaments. If a high levelof varus/valgus constraint is required, coupling component 106 may beused. (See FIG. 2). In the embodiment of knee prosthesis 100 shown inFIG. 2, varus/valgus moments are counteracted by the close fit betweenthe diameter of ball 108 and spherical cavity (168 or 170) inconjunction with the close fit between the diameter of the connectingpost 118 and widths of slot 136 of tibial component 104 and slot 180 ofcoupling component 106, respectively. A high level of varus/valgusconstraint is possible without restricting all other levels of movement,i.e., internal/external rotation, A-P stability and rollback.Conversely, if no varus/valgus constraint is required, couplingcomponent 106 a may be used. (See FIG. 16). Coupling component 106 adoes not resist varus or valgus moment.

Knee prosthesis 100 reduces the A-P laxity (i.e., A-P stability) atimportant points of flexion (i.e., 0 degree to 60 degree of flexion). Inaddition, knee prosthesis 100 constrains varus/valgus movement whilestill allowing internal/external flexion. The amount of varus/valgusconstraint depends of the coupling component (106 or 106 a), which canbe changed by simply swapping out the coupling component instead ofreplacing the tibial component 104 and femoral component 102. Thecoupling component (106 or 106 a) may be changed before the operation orduring the operation. The design of knee prosthesis 100 permits smoothkinematics (flexion/extension, internal/external rotation, rollback) dueto placement of ball 108 with respect to the flexion axis. The design ofball 108 and internal cavity 166 of coupling component 106 allows kneeprosthesis 100 to undergo a natural motion during articulation. Thetibial component 104 (as opposed to ball 108) provides a low frictionarticular surface capable of transferring compressive loads to thetibia. The small ball 108 and coupling component 106 enables a longeranatomic patella track on the anterior flange.

During installation of knee prosthesis 100, the traditional primary cutscan be made on the femur and tibia. Moreover, bone does not need to beremoved from the femur to accommodate a pin as required in a traditionalhinge design. When a pin is employed, the medial and lateral sides ofthe bone have to be resected, whereas, in this design, only theintercondylar areas of the bone have to be resected. Also duringinstallation, coupling component 106 or 106 a can be inserted and fixedto femoral component 102 by sliding extensions 169 along slot apertures159 of femoral component. FIG. 17 shows an alternate embodiment of astabilized knee prosthesis 200 for replacing a natural knee joint. Kneeprosthesis 200 includes a femoral component 202, a tibial component 204,and a coupling component 206 movably connecting femoral component 202 totibial component 204. Femoral component 202 is therefore movably coupledto tibial component 204.

Tibial component 204 includes a tibial baseplate 210 and a tibialbearing insert or component 216. When tibial component 204 is completelyassembled, tibial baseplate 210 supports tibial bearing insert 216 (seeFIG. 24). As seen in FIG. 19, tibial baseplate 210 may have asubstantially oblong shape matching the proximal tibia and includes anintercondylar support 211 for supporting, among other things, astabilizing post 218 (see FIG. 21). Support 211 has an opening or cavity225 dimensioned for receiving at least a portion of a support post 290(see FIG. 22). Further, support 211 has a bore 227 (see FIG. 18) locatedwithin cavity 225. Bore 227 is dimensioned to receive a portion ofsupport post 290, as discussed in further detail below. In addition tosupport 211, tibial base plate 210 has a first bone contacting bottomportion 212 for engaging the proximal tibia and a second opposite topportion 214 for supporting tibial bearing insert 216 (see FIG. 24). Thetop portion 214 of tibial baseplate 210 includes a rim or wall 226enclosing cavity or opening 219. Opening 219 is dimensioned to receiveat least a portion of tibial bearing insert 216. Wall 226 has medial andlateral sides 215 and 217, which are oriented in directly oppositerelationship with respect to each other and are oriented medially orlaterally depending on whether the baseplate 210 is on the left or righttibia. Tibial baseplate 210 further includes extensions 221 and 223protruding from wall or rim 226. Extensions 221 and 223 facilitate asnap connection between tibial baseplate 210 and tibial bearing insert216.

With reference to FIG. 23, the tibial bearing insert 216 of tibialcomponent 204 allows articulation of femoral component 202 relative totibial component 204 and includes a first distally facing side 228 forsecurely engaging the second proximally facing side 214 of tibialbaseplate 210 and a second side 230 for providing a bearing surface forsupporting at least a condylar portion of femoral component 202. Firstside 228 may have posterior recessed grooves or slits 229 for securelyreceiving extensions 221 of tibial bearing baseplate 210 and anteriorrecessed grooves or slits 231 (see FIG. 17) for securely receivingextensions 223 of tibial bearing baseplate 210. Second side 230 has amedial condyle track 232 and a lateral condyle track 234. Each condyletrack 232, 234 is adapted to receive and support a condyle of femoralcomponent 202. Tibial bearing insert 216 defines a clearance slot 236between the condylar tracks 232 and 234. Clearance slot 236 isdimensioned for securely receiving stabilizing post 218 (see FIG. 25).

Referring again to FIGS. 17 and 18, coupling component 206 includes astabilizing post 218 and a support post 290. Support post 290 couplesstabilizing post 218 to tibial component 204 and reinforces stabilizingpost 218 to resist bending forces developed during flexion. Stabilizingpost 218 allows articulation of femoral component 202 relative to tibialcomponent 204 and may be wholly or partly made of polyethylene or anyother suitable polymer. Suitable polymers include, but are not limitedto, polyether ether ketone (PEEK) and ultra high molecular weightpolyethylene (UHMWPE). Moreover, stabilizing post 218 has a rounded end295, an open end 297, an inner channel 291 dimensioned to receivesupport post 290, and a bumper or protrusion 293 located on an anteriorsurface 281. The rounded end 295 of stabilizing post 218 may have asubstantially hemispherical or spherical shape. Protrusion 293 ispositioned between the rounded end 295 and the open end 297 ofstabilizing post 218 closer to the upper surface of bearing insert 216(increasing bending resistance) and can engage an anterior wall 254 of ahousing 248 of femoral component 202 during hyperextension of the kneeto minimize edge loading of the post 218 in that region. The open end297 of stabilizing post 218 has an aperture 299 leading to inner channel291. Aperture 299 is dimensioned for receiving at least a portion ofsupport post 290. The open end 297 of stabilizing post 218 further has arectangular notch or opening 283 on its anterior side. Rectangularopening 283 is dimensioned for receiving at least a portion of supportpost 290, as discussed further below. When support post 290 andstabilizing post 218 are connected to tibial component 204, stabilizingpost 218 and support post 290 define an oblique angle relative to thetibial component 204. Stabilizing post 218 may have different sizes andthicknesses. The size of stabilizing post 218 may affect thevarus/valgus constraint of the knee prosthesis 200. For example, thevarus/valgus constraint of knee prosthesis 200 may be increased byincreasing the thickness of the stabilizing post 218.

Referring to FIG. 22, the support post 290 of coupling component 206 maybe made of any substantially rigid material, such as a suitable metal,and enhances the structural integrity of stabilizing post 218. Suitablemetals include, but are not limited to, stainless steel, titanium,titanium alloy, cobalt-chromium-molybdenum alloys (e.g.,cobalt-chromium-molybdenum alloy sold under the trademark Vitallium®owned by Stryker Corporation). Support post 290 may have different sizesor heights. The height of support post 290 should be directlyproportional to the size of the knee prosthesis 200. For example, largerknee prostheses 200 should include taller support posts 290. In oneembodiment, support post 290 includes a first elongated member 292, asecond elongated member 294, and a supporting connector 296 attachingfirst elongated member 292 and second elongated member 294. Support post290 may be a monolithic structure or a modular structure made of two ormore separate pieces or parts. For instance, support post 290 may beformed of three separate or discrete parts, namely the first elongatedmember 292, the second elongated member 294, and the supportingconnector 296. Each of first elongated member 292 and second elongatedmember 294 may be substantially similar and sized to be received withininner channel 291 of stabilizing post 218. In one embodiment, firstelongated member 292 and/or second elongated member 294 may have asubstantially cylindrical shape. Regardless of their shape, the firstelongated member 292 and/or second elongated member 294 is dimensionedto pass through bore 227 (see FIG. 18) of tibial baseplate 210. Firstelongated member 292 may have a first end 285 attached to supportingconnector 296 and a second end 287 with a tapered region 289. Secondelongated member 294 also has a first end 271 attached to supportingconnector 296 and a second end 273 with a tapered region 275. Supportingconnector 296 may have a substantially elliptical cross-section and isdimensioned to be received within cavity 225 of tibial baseplate 210.When knee prosthesis 200 is completely assembled, supporting connector296 is located within cavity 225 of tibial baseplate 210, one elongatedmember 292 or 294 is positioned along bore 227, and another elongatedmember 292 or 294 extends through inner channel 291 of stabilizing post218.

With reference to FIG. 20, femoral component 202 has a first or proximalside 238 for securely engaging a distal femur and a second or distalside 240 forming a condylar bearing surface. The second side 240 offemoral component 202 includes a first or medial condyle 242 and asecond or lateral condyle 244. Each of first condyle track 232 andsecond condyle track 234 of the tibial component 204 are configured toreceive first and second condyles 242, 244, respectively. The secondside 240 of femoral component 202 further includes a patella track (notshown) between first and second condyles 242, 244 and is adapted toreceive a patellar implant (not shown). The first side 238 of femoralcomponent 202 includes a housing 248 between the first and secondcondyles 242, 244. Housing 248 may be monolithically formed with femoralcomponent 202 and includes an anterior wall 254 and a proximal wall 256as seen in FIG. 17. The proximal wall 256 of housing 248 includes a cam278 configured to engage stabilizing post 218 upon articulation offemoral component 202 relative to tibial component 204. Housing 248forms an internal pocket or cavity 266 dimensioned to receive therounded end 295 of stabilizing post 218. Therefore, at least a portionof cavity 266 may have a substantially spherical shape.

With reference to FIG. 24, a completely assembled knee prosthesis 200may be employed to replace a knee joint as described above with respectto the knee prosthesis 100. To assemble knee prosthesis 200, a user ormanufacturer may first attach tibial bearing insert 216 to tibialbaseplate 210. Tibial bearing insert 216 can be locked to tibialbaseplate 210 by inserting extensions 221 and 223 in slits 229 and 231,respectively. Support post 290 is then introduced through clearance slot236 of tibial bearing insert 216 until support connector 296 is securelypositioned in cavity 225 of tibial baseplate 210. At this point, oneelongated member (292 or 294) of support post 290 is located in bore 227of tibial baseplate 210. The other elongated member (292 or 294) ofsupport post 290 extends away from tibial component 204. Stabilizingpost 218 is placed over the exposed elongated member (292 or 294) ofsupport post 290 such that said elongated member is positioned in innerchannel 291. Alternatively, stabilizing post 218 may be placed oversupport post 290 before attaching support post 290 to tibial bearinginsert 216. In addition, the protrusion 293 of stabilizing post 218should face the anterior portion of tibial component 204, as seen inFIG. 24. Stabilizing post 218 and support post 290 may either beassembled at the time of surgery or preassembled at the factory. Then,femoral component 202 is placed over the stabilizing post 218 such thatthe rounded end 295 of stabilizing post 218 is situated within thecavity 266 of housing 248.

After knee prosthesis 200 has been assembled, femoral component 202 canarticulate relative to stabilizing post 218 about a wide range offlexion degrees. As seen in FIG. 24, protrusion 293 contacts theanterior wall 254 of housing 248 during hyperextension of the knee,thereby minimizing edge loading of stabilizing post 218 in that contactregion.

FIGS. 25 and 26 show an alternate embodiment of knee prosthesis 200,wherein tibial bearing insert 216 and stabilizing post 218 are made froma single piece. In other words, stabilizing post 218 is monolithicallyor integrally formed with tibial bearing insert 216. In this embodiment,support post 218 includes only one elongated member 292 and does notinclude a support connector. Elongated member 292 is dimensioned to bereceived within inner channel 291 of stabilizing post 218 and enhancesthe structural integrity of stabilizing post 218. In a furtherembodiment, stabilizing post 218 may be integrally or monolithicallyformed with tibial baseplate 210.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A knee prosthesis for implanting in a kneejoint, comprising: a femoral component; a tibial component including aball, the femoral component being configured to move relative to thetibial component; and a coupling component interconnecting the femoralcomponent and the tibial component, the coupling component defining aninternal cavity including a first spherical end portion and a secondspherical end portion, the internal cavity being dimensioned to receivethe ball of the tibial component, wherein the ball is repositionedbetween the first spherical end portion and the second spherical endportion of the internal cavity upon movement of the femoral componentrelative to the tibial component, and an internal surface of thecoupling component includes a cam adjacent the internal cavity, the camprojecting outward from the internal surface and being configured toguide repositioning of the ball between the first spherical end portionand the second spherical end portion when the femoral component movesrelative to the tibial component.
 2. The knee prosthesis according toclaim 1, wherein the coupling component substantially encloses the ballof the tibial component.
 3. The knee prosthesis according to claim 1,wherein the first and second spherical end portions have substantiallysimilar diameters.
 4. The knee prosthesis according to claim 1, whereinthe internal cavity includes a longitudinal portion interconnecting thefirst and second spherical end portions.
 5. The knee prosthesisaccording to claim 4, wherein the longitudinal portion of the internalcavity has a substantially cylindrical shape.
 6. The knee prosthesisaccording to claim 5, wherein the longitudinal portion of the internalcavity has a diameter substantially similar to diameters of the firstand second spherical end portions.
 7. The knee prosthesis according toclaim 1, wherein the tibial component further comprises a baseplate anda post connected to the ball, the post extending away from thebaseplate.
 8. The knee prosthesis according to claim 7, wherein thecoupling component defines a longitudinal opening leading to theinternal cavity and dimensioned to receive the post of the tibialcomponent.
 9. The knee prosthesis according to claim 7, wherein thecoupling component includes a first end and a second end, the second endincluding the cam, such cam being configured to engage the post uponmovement of the femoral component relative to the tibial component. 10.The knee prosthesis according to claim 1, wherein the coupling componentdefines a slot extending therealong.
 11. The knee prosthesis accordingto claim 1, wherein the femoral component includes a medial condyle anda lateral condyle.
 12. The knee prosthesis according to claim 1, whereinthe femoral component includes a housing dimensioned to receive thecoupling component.
 13. The knee prosthesis according to claim 1,wherein the coupling component is formed by a first section and a secondsection joined together.
 14. A knee prosthesis for implanting in a kneejoint, comprising: a femoral component; a tibial component including aball, wherein the femoral component is configured to articulate relativeto the ball of the tibial component; and a coupling component connectingthe femoral component to the tibial component, the coupling componentdefining an internal cavity including a first cavity portion and asecond cavity portion each dimensioned to receive the ball, the firstand second cavity portions being in communication with each other,wherein the coupling component moves upon articulation of the femoralcomponent relative to the tibial component between a first positionwhere the ball is positioned in the first cavity portion and a secondposition where the ball is positioned in the second cavity portion, aninternal surface of the coupling component including a cam adjacent theinternal cavity, the cam projecting outward from the internal surfaceand being configured to guide repositioning of the ball between thefirst cavity portion and the second cavity portion when the femoralcomponent articulates relative to the tibial component.
 15. The kneeprosthesis according to claim 14, wherein the femoral componentsurrounds at least a portion of the coupling component.
 16. The kneeprosthesis according to claim 14, wherein the first and second cavityportions have substantially similar diameters.
 17. The knee prosthesisaccording to claim 14, wherein the internal cavity includes alongitudinal portion interconnecting the first cavity portion and thesecond cavity portion.
 18. The knee prosthesis according to claim 17,wherein the longitudinal portion of the internal cavity has asubstantially cylindrical shape.
 19. The knee prosthesis according toclaim 18, wherein the longitudinal portion of the internal cavity has adiameter substantially similar to diameters of the first and secondcavity portions.
 20. The knee prosthesis according to claim 14, whereinthe tibial component further comprises a baseplate and a post connectedto the ball, the post extending away from the baseplate.
 21. The kneeprosthesis according to claim 20, wherein the coupling component definesa longitudinal opening leading to the internal cavity and dimensioned toreceive the post of the tibial component.
 22. The knee prosthesisaccording to claim 20, wherein the coupling component includes a firstend and a second end, the second end including the cam, such cam beingconfigured to engage the post upon movement of the femoral componentrelative to the tibial component.
 23. The knee prosthesis according toclaim 14, wherein the femoral component is positioned at 0 degree offlexion in the first position and at 135 degrees of flexion in thesecond position.
 24. The knee prosthesis according to claim 14, whereinthe femoral component flexes relative to the tibial component along aflexion axis.
 25. The knee prosthesis according to claim 24, wherein thecoupling component connects the femoral component to the tibialcomponent so that a flexion of the femoral component relative to thetibial component along the flexion axis ranges between 0 degree offlexion and 150 degree of flexion.